An aromatic polycarbonate is excellent in, for example, transparency, mechanical properties, thermal properties, electrical properties, and weatherability, and has been used in an optical molded article, such as a light-guiding plate, a lens, or an optical fiber, through the utilization of its characteristics. However, the light transmittance of the polycarbonate serving as one of the indicators representing its transparency is lower than that of, for example, a polymethyl methacrylate (PMMA). Therefore, a surface light source body including a light-guiding plate made of the aromatic polycarbonate and a light source has a problem in that its luminance is low. Accordingly, the development of a method of improving a luminance and a light transmittance in the light-guiding plate made of the aromatic polycarbonate has been progressing.
In PTL 1, in order to provide a polycarbonate resin composition for a light-guiding plate that is free from becoming opaque and being reduced in transmittance, and that has a satisfactory transmittance and a satisfactory hue, there is a disclosure of an aromatic polycarbonate resin composition for a light-guiding plate obtained by incorporating, into an aromatic polycarbonate resin, a polyoxyalkylene glycol containing a polyethylene glycol or a polypropylene glycol as a main component, or a fatty acid ester thereof.
However, in the method of PTL 1, the heat resistance of the polyoxyalkylene glycol is low, and hence when the composition is molded at a temperature of more than 320° C. or its molding cycle becomes longer, its yellowing becomes serious to largely reduce its luminance and light transmittance, and the reductions may adversely affect the optical performance of a light-guiding product. Further, when the molding is performed at a temperature of more than 340° C., a silver occurs on the surface of a molded article owing to the decomposition gas of the polyoxyalkylene glycol to preclude the article from functioning as the light-guiding product. Accordingly, a temperature increase for an improvement in flowability of the composition is limited, and hence the composition cannot be molded into a thin-walled and large-area light-guiding plate. Therefore, the method is applicable only to some molding materials for small light-guiding plates to be molded at a low temperature around 280° C., and hence its practical range is narrow and insufficient.
In PTL 2, in order to provide an aromatic polycarbonate resin composition capable of resisting molding at high temperature through the alleviation of the insufficient heat resistance serving as a drawback of the method of PTL 1, there is a disclosure of an aromatic polycarbonate resin composition obtained by blending an aromatic polycarbonate resin with a polyoxytetramethylene-polyoxyethylene glycol. According to the method of PTL 2, the composition can be molded in the temperature region of from 280° C. to 340° C. without yellowing.
Meanwhile, in PTL 3, in order to provide a resin composition excellent in heat stability in high-temperature molding and capable of providing a molded article that is excellent in light transmittance and luminance, and that does not cause discoloration or an internal crack after a moist heat resistance test, there is a disclosure of an aromatic polycarbonate resin composition obtained by incorporating a specific diphosphite compound and a specific alicyclic epoxy compound into an aromatic polycarbonate resin. According to the method of PTL 3, the composition can be molded at a temperature of more than 340° C. without yellowing.